The fermentative syntheses of foreign or exogenous oligosaccharides using recombinant microorganisms have recently become of great commercial and industrial interest. In such syntheses, oligosaccharides of interest would be synthesized by enzymatic glycosylation of sugar acceptors mediated by one or more heterologous glycosyl transferases of the microorganisms, and the one or more activated sugar nucleotides necessary for glycosylation would be produced by the same microorganism through overexpressing one or more genes encoding endogenous activated sugar nucleotide producing enzymes. The metabolic pathways of such syntheses require a carbon source which is mainly a simple carbon building block, typically glycerol or glucose (see e.g. WO 01/04341, Priem et al. Glycobiology 12, 235 (2002), Fort et al. Chem. Comm. 2558 (2005), Drouillard et al. Angew. Chem. Int. Ed. 45, 1778 (2006), WO 2010/070104, WO 2012/112777, WO 2013/182206, WO 2014/048439). In some syntheses, lactose can be the carbon source if it also serves as an acceptor (Lee et al. Microb. Cell Fact. 11:48 (2012)). As the microorganisms have been genetically manipulated, antibiotic-resistance selection marker genes have been utilized to separate the transformed microorganisms from the non-transformed ones in the inoculum and the fermentation broth. However, the use of antibiotics has been avoided by integrating the genes coding for enzymes involved in the de novo biosynthesis of the donor sugar in the chromosome of the microorganisms (Baumgartner et al. Microb. Cell Fact. 12:40 (2013)).
Around 50% of wild-type E. coli are able to utilize sucrose as a carbon and energy source, but most of them are pathogenic. The E. coli strains used mainly in industry to synthesize chemical materials cannot live and grow on sucrose (Bruschi et al. Biotechnol. Adv. 30, 1001 (2012)). However, in some cases, sucrose can be a cheaper carbon and energy source. For this reason, attempts have been made to create suck strains of E. coli that can live and grow on sucrose (e.g. Sabri et al. Appl. Environ. Microbiol 79, 478 (2013)) and produce industrially profitable products by them such as amino acids, biofuel, carotenoids etc. (e.g. EP-A-1149911, EP-A-2239336, EP-A-2371952, EP-A-2405006, WO 2010/051849, WO 2012/078311, Kim et al. Biores. Technol. 130, 288 (2013)). However, these suck transformants have generally been less productive than suc− strains (Khamduang et al. J. Ind. Microbiol. Biotechnol. 36, 1267 (2009)).
WO 2012/007481 describes E. coli transformants that express either a sucrose phosphorylase or a sucrose invertase in combination with a fructokinase. Thereby, the microorganism is able to produce 2′-fucosyllactose, utilizing sucrose as its main carbon source. Furthermore, WO 2014/067696 describes an E. coli transformant comprising a csc-gene cluster that enables it to grow on sucrose and produces fucose.
There has been, however, a continuing need for alternative processes for making recombinant oligosaccharides, particularly HMOs, using transformed microorganisms that are able to utilize more effectively sucrose as a carbon and energy source.